1. Field of the Invention
The present invention relates to vehicle air conditioners, especially to a device for controlling the speed of revolution of the blower.
2. Description of the Prior Art
As FIG. 5 shows, a typical vehicle air conditioner according to the prior art consists of a duct 1, a shutter 2 provided at the inlet of the duct, a blower 3, an evaporator 4, a mixing shutter 5, a heater core or radiator 6, a mode switching shutter 7, a defrosting outlet or vent 8, a face level outlet or vent 9, and a foot level outlet or vent 10. The evaporator 4 consititutes a refrigeration circuit together with a compressor 11, a condensor 12, a receiver tank 13, and an expansion valve 14. The revolution of the engine (not shown) is transmitted to the compressor 11 through a magnetic clutch 16.
An A/D converter 17 is provided to convert respective analog signals of the compartment temperature Tr sensed by a compartment temperature sensor 18, the opening .theta. of the mixing shutter 5 sensed by a position sensing potentiometer 19, the sunshine temperature Ts sensed by a sunshine sensor 20, the ambient temperature Ta sensed by an ambient air sensor 21, the evaporator temperature Tm sensed by an evaporator temperature sensor 22, and the desired temperature Td set by a temperature setting device 23 into the corresponding digital signals, which are fed to a controlling device 24.
The controlling device 24 is composed of, for example, a microcomputer and consists of a shutter controlling means 27 for controlling the shutter 2 through a switchng circuit 25 and an actuator 26, a compressor controlling means 29 for controlling the magnetic clutch 16 through a driving circuit 28, a blower controlling means 31 for controlling the blower 3 through a driving circuit 30, a mixing shutter controlling means 34 for controlling the mixing shutter 5 through an actuator 33, a mode switching shutter controlling means 37 for controlling the mode switching shutter 7 through a switching circuit 35 and an actuator 36, and an operational means 38 for computing the total signal T from the respective data Tr, Ts, Ta, Tm, and Td and feeding it to the respective controlling means. The signals from a manual switch 39 for controlling the blower and a water temperature switch 40 for sensing the water temperature of the radiator are also fed to the controlling device 24.
When the evaporator temperature Tm sensed by the sensor 22 reaches a level slightly higher then the frozen point of the evaporator, the compressor controlling means 29 turns off the compressor 11 to keep the temperature of the evaporator 4 constant at the level.
As FIG. 6 shows, the blower controlling means 31 consists of a start controlling section 31A which operates when the blower 3 starts upon start of the engine and an automatic controlling section 31B for controlling the blower 3 based on the total signal T in the automatic control mode. The start controlling section 31A consists of a start controlling section 31C operable at the start time of the heater and a start controlling section 31D operable at the starting time of the cooler.
The automatic control section 31B includes a first setting section 31F responsive to the total signal T to read a driving voltage VS1 from a memory 31E and feed it to the blower 3. As shown in FIG. 6, the driving voltage VS1 takes a high or low status depending on the total signal T for driving the blower 3 in the automatic controlling mode.
As described in Japanese U.M. Patent Kokai No. 59-38105, the start controlling section 31C has a setting means 31H for reading a driving voltage VS2 from a memory 31G at the initial period of a heating operation to set the blower 3 at the number of revolutions corresponding to the voltage VS2. The start controlling section 31D has a setting section 31l for reading a driving voltage VS3 from a memory 31K at the initial period of a cooling operation to set the blower 3 at the number of revolutions corresponding to this voltage VS3. When the driving voltage VS2 or VS3 exceeds the driving voltage VS1, a switching means 31N switches the blower control from the first or second start controlling section 31C or 31D to the automatic controlling section 31B.
As FIG. 7 shows, the driving voltage VS2 from the memory 31G increases as the value M of the following equation (1) EQU M=Td-Tr (1)
decreases, or the compartment temperature Tr increases. Consequently, the number of revolutions of the blower 3 increases as the compartment temperature Tr increases in the initial period of engine start so as to provide a more comfortable heating condition. When the driving voltage VS2 fed to the blower 3 exceeds the driving voltage VS1 from the memory 31E, or EQU M=Td-Tr&lt;.alpha.
where .alpha. is a variable varying with the total signal T, the blower 3 is controlled by the automatic control section 31B in the automatic control mode.
That is, the blower is controlled by the driving voltage VS1 having a characteristic Z, as shown in FIG. 8, which is a function of the total signal T given by the following equation (2): EQU T =(N.multidot.Ts+L.multidot.Tr+M.multidot.Ta+O.multidot.Tm)-K.multidot.Td(2 )
where K, L, M, N, and O are constants. In this way, the number of revolutions of the blower 3 is automatically determined based on the respective temperature signals Td, Tr, Ta, Ts, and Tm. In other words, the blower 3 is controlled by the automatic control section 31B in the automatic control mode after its speed of revolution reaches a predetermined starting level as the compartment temperature Tr is increased by the start control section 31C or 31D. If the automatic control mode is employed from the beginning, a strong blow of cold or hot air can be produced and the number of revolutions of the blower 3 is changed rapidly at the time of engine start, providing an uncomfortable air condition.
We have already proposed the following improved method using the afore-mentioned start control section 31C. In this method, the blower is controlled by the driving voltage having a characteristic such as shown in FIG. 9, in which the operational temperature TP and the blower driving voltage V are taken as abscissa and ordinate, respectively. The computed temperature TP is given by EQU TP=Td+(Tr-25) (3)
where Td is the desired temperature set in the temperature setting device 23 and Tr is the compartment temperature sensed by the sensor 18 disposed in the vehicle compartment.
The driving voltage characteristic l for starting the blower 3 in the heating operation becomes a straight line joining points P1 and P2. The speed of revolution of the blower 3 is increased from the point P1 corresponding to the operational temperature TP1 at which the engine cooling water reached a predetermined temperature (for example, 40.degree. C.). Hereinafter, the operational temperature TP1 at the point P1 is referred to as the sensed operational temperature TP1. Until this point P1, the blower 3 rotates at a low speed with a low voltage applied when the power switch is turned on. The blower 3 rotates at a high speed with a high voltage applied at the point P2 or operational temperature TP2 at which the operational temperature TP is, for example, 16.degree. C. Hereinafter, this operational temperature is referred to as the desired conversion temperature TP2.
When the power switch 9 is turned on, the blower 3 starts to rotate at a low speed. When the engine cooling water for heating the heater core reaches, for example, 40.degree. C., the blower driving voltage increases along the straight line l between the sensed operational temperature TP1 (P1) and the desired conversion temperature TP2 (P2) to increase the speed of the blower 3. The acceleration of the blower can be controlled by adjusting the slope of the line l at the sensed operational temperature TP1 so as to enhance passenger's feeling. Then, the blower is operated in the automatic control mode.
In the above vehicle air conditioner, after the water temperature reches 40.degree. C., the blower can be accelerated in response to an increase of the desired temperature Td or compartment temperature Tr so as to increase slowly the speed of a hot air flow, but there is a delay in operation of the water temperature switch because the water temperature switch is disposed in the vicinity of the heater core instead of sensing directly the water temperature. Consequently, the operational temperature TP becomes high when the compartment temperature is relatively high in the intermediate period or at the time of restarting. As FIG. 9 shows, the point P1 is shifted to a great extent toward the point P2, making a sharp slope la of the driving voltage. As a result, the blower is accelerated too much to provide a comfortable heating condition. This shortcoming is felt especially in a vehicle with a direct injection diesel engine which produces little exhaust heat (or the ambient temperature is very low or the number of passengers is very large) because the temperature of the engine cooling water takes long time to reach 40.degree. C. after the engine starts running.